1. Field of the Invention
The present invention relates to a long light emitting apparatus, provided by connecting a plurality of LED lamps to a flexible conductor, for emitting light approximately equal in brightness in all directions except backward from the bases of the lamps.
2. Description of the Related Art
A conventional long light emitting apparatus has been designed to have a large number of small electric bulbs connected to a long conductor to emit light from the electric bulbs. Such light emitting apparatuses are used as decorative lights applied to streets trees, Christmas trees, etc.
Each of these small lights for the long light emitting apparatus is normally referred to as a filament lamp, and is made of a light emitter of tungsten, opposed electrode foil, etc. covered with a glass bulb. When the bulb is turned on, it emits light by the resistance heat from the tungsten, or by the corona discharge of the opposed electrode foil.
The light is emitted equally in light quantity in all directions except backward from the base (the light is interrupted by the equipment of a socket, a conductor of the bulb, etc.). Therefore, the emitted light can be easily viewed from any direction. Owing to the excellent visibility, the long light emitting apparatus equipped with a large number of electric bulbs connected to a long conductor can be widely used as effective decorative lights both indoors and outdoors, especially as the above described electric decorations in the Christmas season.
However, since each of the above described small bulbs is made of a light emitting unit of tungsten or opposed electrode foil covered with thin glass bulb, it is easily broken when it touches a hard object. Therefore, when the apparatus is stored and used, users should be extremely careful not to break the bulbs, and therefore they feel nervous in handling the bulbs.
Additionally, a filament lamp is normally poor in electro-optical conversion efficiency, and most of the electric power is lost as heat, thereby consuming a large volume of electric power relative to the quantity of emitted light. Therefore, the conventional light emitting apparatus is very uneconomical in simultaneously lighting all of a large number of small filament lamps, even if each of the lamps is very small.
Considering the consumption of electric power only, an LED element is recommended as a light emitter with low electric power consumption. However, the light emitted from the LED element is directional, and indicates an irradiation angle of up to approximately 80 degrees in the front direction of the light emitter. Therefore, LED elements indicating such a narrow optical diffusion are not suitable as decorative lights to be applied to Christmas trees, which are required to emit light in every direction. Actually, the LED elements are normally used as display elements of a device to be viewed from the front. For example, they are applied to time tables provided at stations and airports.
As described above, the LED elements have not been designed to be applied to a long light emitting apparatus to be viewed from all directions. As a result, such a long light emitting apparatus has been equipped with small filament lamps whose irradiation light is non-directional.